Gangliosides are membrane-bound glycolipid molecules that are overexpressed in tumor cells and actively shed into their microenvironment. It has long been proposed that ganglioside abnormalities are linked to the clinical and biological behavior of many types of tumors including neuroblastoma (NB). Our recent work has demonstrated that low or absent expression of complex "b" pathway gangliosides (GD1b, GT1b and GQ1b, termed CbGs) correlates with unfavorable clinical behavior and an aggressive biological phenotype in primary NB tumors. Similarly, high CbG expression is highly predictive of a favorable disease outcome and further substratifies patients that are classified as "good prognosis" by established markers. Further, accumulated evidence from several studies by ourselves and others support the concept that increased cellular CbG content ameliorates the malignant phenotype of NB, implying an inverse correlation between cellular CbG content and in vivo tumorigenicity. We hypothesize that CbGs ameliorate the malignant phenotype in human NB by specifically altering one or more cellular processes that contribute to the malignant behavior of NB cells in vivo. We will test this hypothesis by developing in vitro model systems using human NB cell lines, in which to elucidate the biological consequences of altered CbG expression. Using these models we will determine systematically the influence of modulation of complex ganglioside content on two specific properties that are known to influence the malignant behavior of NB--cell proliferation and cellular differentiation, and the related Trk signaling pathway. Finally, we will determine the influence of modulation of complex ganglioside content in CbG overexpressing NB cells on tumor formation, growth and metastasis by transfection of human NB cells with human GD1b/GM1a synthase cDNA (B3GalT4), followed by evaluation of NB tumor formation, growth and metastasis in a novel (periadrenal) orthotopic routine model. These studies will further elucidate the functional role of complex "b" pathway gangliosides in the formation and progression of human NB specifically, and neuroectodermal tumors in general, and provide a basis for the development of novel therapeutic approaches for this class of tumors.